This invention relates to a monitoring apparatus to monitor the presence of a patient in a supporting structure such as a bed, a chair or like supporting device.
Patients or residents are often restricted to a bed, chair, or other supporting structure for various reasons, primarily related to their well being and safety. Monitoring is significantly important in a restricted free environment for protecting the dignity of people. Additionally, a patient may at times refuse conforming to restrictive requirements, or may accidently or inadvertently attempt to move themselves because they forget the ability to make a rational decision is impaired or the like which may prevent following instructions. If a patient inadvertently or accidentally leaves or attempts to leave a support and immediately returns, it may not be necessary to indicate such a minor occurrence. If they move from the support for any period of time or start to leave, which for some individuals may be on the order of seconds, an alarm may be necessary. This aspect of monitoring would require different response characteristics of the monitoring system. Thus, it may be desirable to minimize and avoid unnecessary reaction to non-adverse movements of one patient, while others may require immediate attention to unauthorized movement. This invention thus also may provide advance notice of a patient or resident leaving a chair or bed before they actually do so.
Further, the monitoring systems are used in rather widely and different environments including atmospheric conditions, and sensor quality may deteriorate with age, changes in the weight of the patient and other similar variables which are widely encountered in the health care field. A most satisfactory system should operate in the various settings and requirements.
Prior art systems have generally used on/off sensing unit for actuating an output alarm unit. For example, U.S. Pat. No. 4,179,692 which issued Dec. 18, 1979 and the related U.S. Pat. No. 4,295,133 which issued Oct. 13, 1981, disclose systems in which on/off switch generates binary signals in response to the movements of the patient to and from the bed. A time may be used to delay an alarm, which also prevents effective advance warning. The latter patent provides a switch which is sensitive to movement within the bed to generate on/off signals reflective of movement within the bed structure. Thus, if a patient is sufficiently restless, movement of the patient creates closure of the switch more often than is considered normal. Charging and discharging of a capacitor is controlled by on and off status of the switch and provides a threshold signal under conditions which are considered sufficiently adverse to trigger an alarm. Various switch systems are illustrated including spring loaded switch units which respond to patient movement, or support members which hold contacts in spaced relation with the contact being deformed by the patient movement to thereby change the switch between on and off status. In all instances, a distinct step movement is required and a pressure sensitive device provides a digital on/off output signal.
A similar system is shown in the more recently issued U.S. Pat. No. 4,700,180 which also discloses a binary signal generating sensor. This system responds whereby a patient lying down on a bed establishes a first switch position. When the patient moves from the bed or even moves to the edge of the bed, the switch changes to its alternate state thereby providing a binary signal similar to that of the other prior art references. The on/off signal, again, is a step function signal in a processing system to respond and provide an appropriate alarm. The '180 patent also discloses a sandwich-type construction with a thin compressible insulating material having a central opening. Contacts are secured to the opposite faces of the insulating mat spanning the opening. The patient lying on the mat compresses the insulating mat and moves the conducting wires into a closed circuit condition. A somewhat similar device is shown in a prior art patent U.S. Pat. No. 4,484,043 which issued Nov. 20, 1984. U.S. Pat. No. 5,144,284 which issued September, 1992 discloses a pressure sensor having foil elements separated by a foam element. With a low voltage applied to the plates, a change in electrical resistance or capacitance is created and detected by the device.
In nursing homes, retirement homes, hospitals and like facilities, various degrees of activities are permitted for different patients. It becomes extremely difficult with present day technology to provide for the necessary monitoring of these various patients with such widely varying characteristics with present day switching systems.
The inventors' analysis and investigation has resulted in a unique realization of the sources of the problem associated with present day devices available for patient monitoring with respect to a given support structure. Generally, the inventors realized that the sensing switches only provides a binary signal generating devices which has limited the response system. In particular, the processing of the on/off switch signals limits the ability to continuously track the movement of the patient. This basic approach, which appears to be uniformly used in the prior art known to the inventors, finds severe limitation on the ability of the system to respond to the varying patient characteristics, and significantly the operating environment within which the patients live and the systems operate.